Robin Roberts revealed Tuesday that she'll undergo her bone marrow transplant this week and she assured fans that she's keeping her spirits up even though her body is weak.

The "Good Morning America" co-host wrote on her personal blog that the transplant -- during which she'll receive bone marrow from her sister Sally -- is scheduled for Thursday morning.

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"The start of last week went well but the daily chemo/treatment caught up to me by the weekend," she wrote. "My body is so weak but not my mind. YOU give me the courage to keep going."

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Roberts said on Sunday she held a gathering at her apartment for "GMA family" members. "The next morning I walked through the hospital doors, with my guardian angels -- mom & dad -- back together and blazing a trail ahead of me." The newswoman's 88-year-old mother, Lucimarian Tolliver Roberts, passed away last month.

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Roberts began a medical leave of absence from "Good Morning America" on Aug. 30 to prepare for the bone marrow transplant, which is intended to fend off the rare blood disorder Myelodysplastic syndrome (MDS) that she contracted during treatment for breast cancer.

The co-host's physician, Dr. Gail Roboz, is scheduled to appear on Thursday's "Good Morning America" to give an update on her condition.